Add failing test for trailing commas in methods

test/acorn/tests-babel.js

@@ -3255,6 +3255,65 @@ test("function log(n, op, val,) { }", {
   features: { "es7.trailingFunctionCommas": true }
 });
 
+test("class Foo { bar(a,) { } }", {
+  type: "Program",
+  start: 0,
+  end: 25,
+  body: [{
+    type: "ClassDeclaration",
+    start: 0,
+    end: 25,
+    id: {
+      type: "Identifier",
+      name: "Foo",
+      start: 6,
+      end: 9
+    },
+    superClass: null,
+    body: {
+      type: "ClassBody",
+      start: 10,
+      end: 25,
+      body: [{
+        type: "MethodDefinition",
+        start: 12,
+        end: 23,
+        static: false,
+        key: {
+          type: "Identifier",
+          start: 12,
+          end: 15,
+          name: "bar"
+        },
+        kind: "method",
+        value: {
+          type: "FunctionExpression",
+          start: 15,
+          end: 23,
+          id: null,
+          params: [{
+            type: "Identifier",
+            name: "a",
+            start: 16,
+            end: 17
+          }],
+          generator: false,
+          body: {
+            type: "BlockStatement",
+            start: 20,
+            end: 23,
+            body: []
+          },
+          expression: false
+        }
+      }]
+    }
+  }]
+}, {
+  ecmaVersion: 7,
+  features: { "es7.trailingFunctionCommas": true }
+});
+
 testFail("log(,);", "Unexpected token (1:4)", {
   ecmaVersion: 7,
   features: { "es7.trailingFunctionCommas": true }